RFR: 8293976: Use unsigned integers in Assembler/CodeBuffer::emit_int*

[Quan Anh Mai]

Assembler/CodeBuffer::emit_int* accept signed int arguments.

- Since we are trying to emit some bit patterns into the code buffer instead of doing integer arithmetics, it makes more sense to use unsigned parameters.

- It makes usage with constants become inconvenient, as an integer literal is positive, a 0xC0 does not fit into an int8_t, resulting in the compiler complaining about lossy implicit conversions, the current solution is manual casting of the constants to unsigned char, which can be converted to int8_t without complaints.

Please have a look and leave some reviews. Thanks very much.

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Commit messages:
 - change signature

Changes: https://git.openjdk.org/jdk/pull/10325/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10325&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293976
  Stats: 29 lines in 2 files changed: 0 ins; 0 del; 29 mod
  Patch: https://git.openjdk.org/jdk/pull/10325.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10325/head:pull/10325

PR: https://git.openjdk.org/jdk/pull/10325